In today's high speed electronic equipment, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, an electrical connector would have little or no effect on the interconnection system from these characteristics. In other words, the system would function as if circuitry ran through the interconnection without any effect on the system. However, such an ideal connector is impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible.
Impedance and inductance control are concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e., involving high frequencies. An example of one such connector is called an "edge card" connector. An edge connector is provided for receiving a printed circuit board having a mating edge and a plurality of contact pads adjacent the edge. Such edge connectors have an elongated housing defining an elongated receptacle or slot for receiving the mating edge of the printed circuit board. A plurality of terminals are spaced along one or both sides of the slot for engaging the contact pads adjacent the mating edge of the board. In many applications, such edge connectors are mounted on a second printed circuit board. The mating "edge" board commonly is called the "daughter" board, and the board to which the connector is mounted is called the "mother" board.
This invention is directed to a method and structure for tuning the impedance of an electrical connector, such as an edge connector, so as to provide an interconnection in an electrical circuit having a given impedance and tuning the connector to substantially match that impedance. The invention also is directed to providing terminals for printed circuit board mounted connectors which reduce the inductance of the connectors.
In addition, cross-talk is a concern in designing an ideal connector, particularly in an edge connector as described above. Heretofore, a myriad of attempts have been made to control cross-talk including installing ground planes in the connector, i.e., by providing some form or another of an integrated grounding structure. Most ground plane systems add complexity to the connector, which results in additional expense. This invention is directed to solving these problems by providing a simple, low cost, low cross-talk connector system while simultaneously controlling the impedance of the connector. This is accomplished by providing significantly larger ground terminals than signal terminals, thus optimizing the performance of each, in combination with a particular alternating array of such terminals.